A monoclonal antibody core facility was created at the inception of this program project to produce reagents necessary for advancement of much of the research of the program. Monoclonal antibodies are fundamental to the cellular and molecular biologic approaches that the program scientists routinely use. Since the original funding period and the previous two competitive renewals, the monoclonal antibody core has generated many monoclonal antibodies that have contributed to the success of the program. In addition to the generation of novel monoclonal antibodies, the core has collected many hybridomas from the public domain that are particularly useful to the program scientists. In this renewal application, we propose to expand the scope of the monoclonal antibody core component B to include the necessary equipment and support staff to facilitate the identification of protein partners physically associated with specific proteins under study by program members. For some time now, immunoprecipitation for a viral protein followed by separation in an SDS-polyacrylamide gel and staining with Coomassie or colloidal silver has become a useful and practical technique for identification of associated proteins. In addition, use of epitope tagged versions of viral and cellular proteins enables the program members to identify associated proteins of practically any gene. Recent innovations and technical advances have made the large-scale identification of associated protein complexes feasible and practical. The increased availability and sensitivity of mass spectroscopy has reduced the amount of protein required for identification and the sequencing of the human and murine genomes now makes protein identification from partial sequences practical. As described in many of the specific projects, the use of this technology has facilitated progress in many areas, and it is clear that program scientists will benefit by having a dedicated resource that will facilitate preparation of suitable cells, preparative scale growth of cells, preparative scale immunoprecipitation, and sample preparation for mass spectroscopy.